Use of bacteria in oil recovery has been under consideration for many years. For example, U.S. Pat. No. 2,413,278 Zobell proposes the use of certain anaerobic bacteria to aid in displacing oil from oil-bearing formations. Most work dealing with the use of bacteria in oil-bearing formations has dealt with anaerobic bacteria since it is believed most such formations contain little or no dissolved oxygen. However, there is no consensus about how much oxygen is present in connate water in a reservoir, and to what extent anaerobic bacteria can use oxygenated and nonoxygenated hydrocarbons as a source of carbon and energy. Whether or not such growth occurs may be a function of the composition of the crude oil in situ. As noted in U.S. Pat. No. 3,332,487, Jones, because they rely on the slow low-energy reactions, anaerobic bacteria cannot attack the low molecular weight hydrocarbons containing less than about 10 carbon atoms per molecule.
Theoretically, microorganisms are believed to achieve increased oil recovery by one or more of the following mechanisms: (a) reducing viscosity by degrading higher molecular weight hydrocarbons, thereby producing carbon dioxide which is dissolved into the remaining in-situ oil, (b) producing organic acids which dissolve cementing materials in the formation thereby creating flow passages, (c) producing surfactants or (d) physically displacing the oil adhering to particles of sand in the formation. These theses have been proposed, among others, in the following U.S. patents and publications: U.S. Pat. No. 2,907,389, Hitzman; U.S. Pat. No. 3,032,472, Hitzman; U.S. Pat. No. 2,660,550, Updegraff, et al.; Petroleum Microbiology, 1967, Elsevier Publication Co.; "The Role of Microorganisms in Secondary Oil Recovery", Proc. Chem. Specialties Manufacturers Assn., Vol. 55, Page 125, 1958; and "Bacterial Release of Oil", World Oil, Pages 36-47, 1947.
In addition, the use of microorganisms to enhance sweep efficiency in waterfloods has been proposed wherein the microorganisms would plug the most porous portions of the reservoir, thereby reducing the tendency of water to "finger" through the reservoir.
It has been suggested that there are no viable naturally-occurring microorganisms in oil bearing formations, so that any existing microorganisms in such formations have invaded as contaminants of the water used in waterfloods, or as contaminants of the water in active aquifers underlying the oil bearing formation which invades the formation after substantial oil production has taken place. Numerous proposals have been made to introduce microorganisms into oil-bearing formations to either supplement existing microorganisms or to initially colonize the formation. However, these techniques have been unsuccessful because the microorganisms tend to be filtered out at or near the formation face, resulting in severe flow restriction into the formation, or plugging.
It is known that microorganisms can and will grow under the environmental conditions existing in a typical oil bearing formation if proper nutrients are available. Nutritionally, oil and formation brine are deficient in usable sources of both nitrogenous- and phosphorus-containing compounds, which tends to prevent growth of most microorganisms, or at best permits growth at a very slow rate. Since microorganisms require water and are generally holophytic (they require their nutrients in solution), and since crude oil is not miscible with water, growth of microorganisms must take place primarily at the oil-water interface. All necessary elements and water must be present for growth and metabolism to take place. An adequate carbon and energy source is readily available in the reservoir in the form of crude oil, so that if proper nutrients are provided growth of the microorganisms can be stimulated.